P947: COMPARATIVE EFFECTIVENESS OF ORAL IXAZOMIB-LENALIDOMIDE-DEXAMETHASONE (IRD) AFTER INITIAL BORTEZOMIB (V)-BASED INDUCTION VS PARENTERAL V-BASED THERAPY IN NEWLY DIAGNOSED MULTIPLE MYELOMA (NDMM)
Authors: R. M. Rifkin, C. L. Costello, R. E. Birhiray, S. Kambhampati, J. Richter, R. Abonour, H. C. Lee, Y. J. Kim, K. Ren, D. M. Stull, D. Cherepanov, K. Bogard, S. J. Noga, S. Girnius
Journal: HemaSphere (2022)

Background: Long-term proteasome inhibitor (PI)-based treatment can improve outcomes for patients (pts) with multiple myeloma (MM). However, prolonged parenteral PI therapy (e.g. with V) can be challenging to achieve in routine clinical practice, and outcomes for pts are often poorer in this setting compared with clinical trials. The phase IV, community-based, single-arm US MM-6 study (NCT03173092) is assessing in-class transition (iCT) from V-based induction to all-oral IRd in transplant ineligible NDMM pts treated in routine clinical practice, with the objective of increasing the duration of PI-based treatment while maintaining quality of life. INSIGHT MM is the largest global, prospective, observational study of MM pts (>4,200), and provided a subset of patients as the comparator cohort. This enabled assessment of iCT vs V-based therapy in NDMM pts in routine clinical practice in the US. Aims: To examine the comparative effectiveness of IRd following initial V-based induction (3 cycles; US MM-6 pts; ‘IRd’ cohort) vs continued V-based therapy (INSIGHT MM pts; ‘V-based’ cohort) in NDMM pts. Methods: A secondary analysis of non-transplant eligible US NDMM pts with ≥stable disease after 3 cycles of V-based induction and baseline Eastern Cooperative Oncology Group performance status (ECOG PS) of 0, 1 or 2 from the US MM-6 (Manda CLML 2020) and INSIGHT MM (Costello Future Onc 2019) studies was performed. Study outcomes included first-line duration of treatment (DOT), overall response rate (ORR), progression-free survival (PFS), overall survival (OS), and reasons for treatment discontinuation. All analyses were weighted using the inverse probability of treatment weighting (IPTW) approach to reduce the imbalance of potential confounding factors between the two cohorts (adjusted analyses). Kaplan–Meier methods were used to examine DOT, PFS, OS, and associated 95% confidence intervals (CIs); the log-rank test was used to compare distribution of time to events. The Clopper-Pearson method was applied to estimate 95% CIs for ORR. Statistical significance was evaluated at alpha=0.05. Results: 100 pts from the IRd cohort (MM-6) and 111 pts from the V-based cohort (INSIGHT) were included. After IPTW, in the IRd vs V-based cohorts: median age was 75.0 vs 74.8 yrs; 56.7 vs 51.3% of pts were male; 37.4 vs 29.1% had an ECOG PS of ≥2; 48.8 vs 41.4% had International Staging System stage III at initial diagnosis, and 79.5/17.7/2.8 vs 77.3/19.5/3.1% pts had received VRd/ V-cyclophosphamide-d (VCd)/ VRCd as initial induction therapy. Adjusted ORRs in the IRd vs V-based cohorts were 74.1 (95% CI 66.0–82.2) vs 57.5% (95% CI 47.9–67.1; p<0.0001). After a median follow-up of 20.3 and 15.8 months in the IRd and V-based cohorts, respectively, DOT was 10.8 (95% CI 6.5–24.4) vs 5.3 months (95% CI 4.3–7.0; p<0.0001) (see Figure). Median PFS was not estimable (NE) in either cohort; 24-month PFS rates were 85.7 (95% CI 68.1–94.0; IRd cohort) vs 76.5% (95% CI 62.6–85.8; V-based cohort). Median OS was NE in either cohort; 24-month OS rates were 94.0 (95% CI 77.7–98.5; IRd cohort) vs 84.9% (95% CI 70.6–92.6; V-based cohort). In the IRd and V-based cohorts, 16.8 and 16.9% of pts discontinued IRd and V, respectively, due to an adverse event. Image:Summary/Conclusion: US MM-6 NDMM pts who transitioned to IRd after 3 initial cycles of V-based induction had a significantly higher ORR and longer DOT compared with pts who received continued V-based therapy in INSIGHT MM. The results suggest that iCT from continued V-based therapy to all-oral IRd may improve outcomes in pts treated at community oncology clinics.